172 



THE AMERICAN MONTHLY 



[September, 



Beale pictures microscopic fungi 

 smaller than that dimension. So it 

 is worth while to consider the likeli- 

 hood of our ever being able to see 

 an atom or a molecule. Accord- 

 ing to Maxwell's measurements an 

 atom of hydrogen has a diameter 

 of about one two-millionth of a 

 millimeter. A molecule may be 

 made up of almost any number of 

 atoms to a thousand or more. A 

 molecule of alum has an hundred 

 atoms, one of albumen nine hundred, 

 and so on. If such groups of atoms 

 are compared in their dimensions, 

 their relative diameters would be 

 as the cube root of their number of 

 atoms, and the alum would be four 

 and six-tenths times the diameter 

 of the hydrogen molecule, and the 

 albumen would be nearly ten times 

 this. That would bring the dia- 

 meter of the latter down to the two- 

 hundred -thousandth of an inch. If 

 a good microscope will show a point 

 but one four-thousandth of a milli- 

 meter, its magnifying power would 

 have to be increased but lifty times 

 in order to show the molecule as a 

 point, while an hundred times would 

 probably reveal something of its 

 structure, if dimension was the 

 only condition required. But we 

 know that what we call heat is the 

 vibratory motion of these atoms and 

 molecules, and, moreover, these 

 vibrations take place at so rapid a 

 rate as to strain our mathematical 

 methods to express it, Avhile the 

 result among the atoms and mole- 

 cules of this vibratory movement is 

 to give them a greater or smaller 

 latitude of movement,— elbow room, 

 which is called their free path. It 

 varies, being greatest in gases and 

 least in solids. In a gas like hy- 

 drogen, at the temperature of zero, 

 this free path is about two hundred 

 times the diameter of the atom, and 

 in water, according to Mr. Hodge's 

 calculations, it is less than the diame- 



ter of the ^molecule. In a micros- 

 cope, motion is magnified as well as 

 the object, and the swifter a thing 

 moves the more difficult it is to see it. 

 The movements of a molecule must 

 prevent us from seeing it, even 

 though our microscopes might 

 otherwise reveal it. But there 

 is still another reason why we can- 

 not see the molecules ; — they are 

 transparent. The sunlight streams 

 through our atmosphere, and does 

 not heat it, and we cannot see it ; 

 if a molecule of oxygen were ten 

 times larger than it is, and it could 

 be grasped and held still in the field 

 of the microscope, there is no rea- 

 son to suppose that it could be seen, 

 because it is perfectly transparent. 

 In passing, we may remark, for 

 the satisfaction of those who have 

 fine objectives and who cannot make 

 the lines of Nobert's bands, or the 

 markings of A. pdluoida come out 

 " like pickets on a fence " that in 

 reality such an expression is very 

 much of an exaggeration. The most 

 that can be done with such objects, 

 is to make the lines quite distinct, 

 so that any person can see them by 

 careful focussing. 



Method of Preparing and 



Mounting Wings of Mi- 



cro-lepidoptera.* 



BY C. H. FERNALD. 



For a long time I have been 

 seeking some method, by means 

 of which, the wings of the micro- 

 lepidoptera could be prepared, so 

 that the venation could be studied 

 under the compound microscope, in 

 a manner that would leave no doubt 

 of the presence or absence of the 

 faintest vein in the whole wing- 

 structure. 



The removal of the scales by me- 



* Read before the Sub-section of Micros- 

 copy of the A. A. A. S. 



